Prior to the present invention, geothermal wells were provided with at least one shutoff valve at the surface wellhead and since most such geothermal wells produce sulfur gases which are very corrosive, they generally are provided with two shutoff valves at the surface wellhead. The inclusion of two valves allows the lower one to remain open and to be used only when the upper one is to be replaced or repaired.
While no pertinent prior art is known regarding the use of a set packer to close off a geothermal well string to allow the changing of the wellhead shutoff valve, similar structure has been suggested in an oil well to allow closure of the production string below the Christmas tree to allow removal and replacement of the master valve. Such structure is disclosed in U.S. Pat. No. 3,366,181 issued Jan. 30, 1968. This patent teaches the use of a lubricator and a pressure-operated piston for moving a packer into a well tubing below the master valve, so that the packer can be set allowing the master valve to be replaced. This patent discloses both mechanical and hydraulic set packers, and also suggests that, if desired, the tubing and rod connections to the packer can be removed with the packer set in the tubing below the master valve, and after the master valve has been repaired or replaced, the tubing and rod can be inserted to recover the packer.
There is nothing in the aforementioned patent to suggest that a packer could be run into a geothermal well bore and set responsive to the pressure in such well bore to allow the wellhead valve to be changed or repaired.